Peripheral structure for monolithic power device This invention concerns a peripheral structure for a monolithic power device.
Conventional integrated circuits usually differentiate themselves by the layout of masks. They are thus frozen vertically and therefore little suited for power integration evolution. Consequently, in order to create new power functions, structures made of technological bricks compatible among themselves, are used preferably.
Thus, integrated components for monolithic power device in planar technology are known. It is essential that such components exhibit good voltage handling, i.e. they have a maximum electric field before avalanche breakdown that is sufficiently high to sustain the voltages desired, while remaining smaller than the critical electric field. The maximum electric field must be controllable when designing and manufacturing the component.
This control relies for the whole semi-conductor power devices known on so-called xe2x80x98guardxe2x80x99 solutions, based upon a spread of equipotential lines at the surface of the component and at the junction levels.
Thus, mesa-type techniques consist of mechanical chamfering of a junction to be protected. However, these techniques are hardly compatible with planar processes enabling the realisation of integrated complex power devices. Moreover, it excludes MOS technology processes, such as IGBT (Insulated Gate Bipolar Transistor) bipolar-MOS or MCT (MOS Controlled Thyristor) thyristor-MOS technologies.
Other guard techniques implement guard rings, field electrodes or field plates, semi-resistive layers or P-junction terminations (JTExe2x80x94Junction Termination Extension). The junction termination type technique, notably, consists of an implantation of a little doped P-region, all around a main junction to be protected and in contact with the said junction. The integrated components using these different guard techniques comprise generally insulating boxes formed laterally in the component and with a shrunk central portion, as well as a stop channel for the potential lines between the main junction and one of the diffusions of the insulating box.
A shortcoming of these guard techniques is that they require a minimum surface in order to control the maximum electric field. Moreover, the manufacture is made more complicated by the necessity of implanting a stop channel. The components using these guard techniques exhibit moreover dissymmetrical voltage handling and therefore constitute technological bricks with reduced reach.
In particular, certain devices exhibit a rear-faced junction, connected physically to lateral insulating boxes, and a front-faced junction, protected by one of the guard techniques and surrounded laterally by stop channels. When the front junction is reverse-biased, the equipotential lines are blocked at the stop channels and do not reach the insulating boxes, whereas when the rear junction is reverse-biased, the equipotential lines rise towards the front face through the insulating boxes.
Besides the shortcomings mentioned, this realisation only enables to introduce elementary electric functions in the box delineated by the rear junction.
This invention concerns a peripheral structure for a monolithic power device with smaller space requirements than the components known for equal value of the critical electric field and enabling the implantation of electric functions at the front face and at the rear face.
The structure of the invention is compatible with a planar technology and enables good control of the electric field.
The invention also concerns such a peripheral structure that does not require any stop channels and that can be used with a MOS technology.
The peripheral structure according to the invention can also enable to sustain symmetrical voltages and thus be particularly supple to be used as a technological brick. This brick enables voltage symmetrisation of existing power components, such as power bipolar transistors, thyristors or IGBT components, but also the design and realisation of new components or of new power electric functions.
To that effect, the invention concerns a peripheral structure for monolithic power device comprising:
a substrate with a first doping type,
a front face fitted with a connection with a cathode,
a rear face fitted with a connection with an anode,
a first junction adjoining one of the faces, whereas this junction is reverse-biased when a direct voltage is applied between the anode and the cathode,
a second junction adjoining the face opposite to the face corresponding to the first junction, whereas this junction is forward-biased when a direct voltage is applied between the anode and the cathode,
at least one insulating box with a second type of doping, connecting the front and rear face and disconnected electrically from the first junction.
The structure is such that when a reverse voltage is applied between the anode and the cathode, creating equipotential voltage lines, the insulating box enables to distribute the equipotential lines in the substrate.
According to the invention, the insulating box is disconnected electrically from the second junction and the peripheral structure is such that when a direct voltage is applied between the anode and the cathode, generating equipotential voltage lines, the insulating box enables to distribute the said equipotential lines in the substrate.
Thus, conversely to known guard techniques, the insulating box(es) fulfil in the invention a distribution function of the equipotential lines in the substrate, i.e. in the volume of the structure, in both biasing directions. Thanks to that distribution, a stop channel proves superfluous and the sizes of the component can be reduced with respect to the existing ones. Besides, electric functions can be implanted on both front and rear faces. Indeed, the anode and the cathode are not in electrical contact with the insulating boxes.
The structure is also capable of sustaining symmetrical voltages. These voltages range for instance between 600 and 1200 V. In some embodiments, they reach values between 4000 and 5000 V.
Preferably, the peripheral structure comprises two lateral insulating boxes, arranged symmetrically with respect to the junctions. However, according to an embodiment variation, it comprises a single lateral insulating box on one side of the junctions, whereas another technique is used on the second side.
The peripheral structure of the invention is used advantageously in a functional integration mode, for which the power function grows out of electrical interactions between arranged and sized semi-conductor regions and also out of surface interconnections. This integration mode is particularly suited to high voltage applications, notably for connections to an electrical energy distribution network calling for symmetrical voltage handling.
According to another embodiment, the peripheral structure according to the invention is implemented in a xe2x80x98smart-powerxe2x80x99 type monolithic power integration mode, for which insulating techniques are injected into the substrate in order to differentiate regions allocated to (high voltage) power functions and regions sustaining circuits for controlling and processing the signals and the (low voltage) information.
The junctions define main boxes with the second doping sign and each delineated by the corresponding junction and by the adjoining face.
Preferably, these main boxes are peripheral.
In a preferred embodiment, the substrate is of N-type and the main box and the insulating box are of P-type. The junction is then adjacent to the front face.
In another embodiment, the substrate is of P-type and the main box and the insulating box are of N-type, whereas the junction is then adjoining to the rear face.
Preferably, the insulating box is little doped and the boxes are highly doped.
In a preferred embodiment, the insulating box is made of a highly doped insulating vertical wall and the component comprises at least one small dose implantation zone of the second doping type, adjacent to that wall and to one of the front and rear faces and arranged between the wall and one of the junctions.
This embodiment of the insulating box and of its vicinity is particularly suited for the insulating box to be able to fulfil its distribution function of the equipotential lines in the substrate. It enables to gain more surface, whereas the insulating box may be reduced in width in relation to the boxes used in the known components. For exemplification purposes, the insulating box is approximately 5 xcexcm in width.
Preferably, the insulating wall is substantially rectangular in shape.
Thereunder, the expression xe2x80x98localised metallizationxe2x80x99 designates metallization of the front or rear faces that is localised to the connection associated with that face, and which therefore has a little length with respect to the length of the said face. The expression xe2x80x98extended metallizationxe2x80x99 refers to non-partial metallization of one of the front or rear faces, i.e. covering a portion of that face non-localised to the connection associated with that face. Preferably, field oxides cover the rear and front faces with the exception of zones localised to the connections. When one of these faces is metallized locally, the said face then covers only the corresponding localised zone, whereas when one of these faces shows extended metallization, the said face also covers partially the corresponding field oxide.
Three preferred embodiments can therefore be distinguished according to whether extended metallization is carried out on none of the front or rear faces, on the rear face or on both rear and front faces. These three preferred embodiments combine with the insulating vertical wall with a small dose neighbouring implantation zone.
In a first embodiment, the peripheral structure comprises:
at least one small dose implantation zone of the second type of doping adjacent to the first junction and the corresponding face and arranged between the first junction and the wall,
at least one second small dose implantation zone of the second type of doping adjacent to the second junction and the corresponding face and arranged between the second junction and the wall,
the implantation zones adjacent to the wall, respectively adjoining the front and rear faces.
Thus, the structure comprises in the vicinity of each of the front and rear faces and going from one junction to a lateral face: the main bow delineated by the junction adjoining the front or rear face, the adjacent small dose implantation zone, a zone without any implantation, the small dose implantation zone adjacent to the wall, and the insulating wall.
This structure is suited to localised metallization of both front and rear faces.
The structure has then preferably a symmetrical configuration with respect to a plane parallel to the front and rear faces and halfway between these faces. Symmetry of voltage handling is thereby improved.
Preferably, the structure comprises two lateral insulating walls fitted with small dose implantation zones in front and rear faces, and two front and rear main boxes, each flanked laterally by two small dose implantation zones.
This first embodiment of the peripheral structure is particularly interesting for its low cost of manufacture and the gain in surface that it enables to obtain.
In a second of the three embodiments mentioned above, the structure comprises:
a rear field plate covering the whole rear face, and
at least one first small dose implantation zone of the second type of doping adjoining the front face and at the corresponding junction.
Moreover, the implantation zone adjacent to the wall is adjacent to the front face.
Thanks to this realisation, we can obtain symmetrical voltage handling in spite of a substantially dissymmetrical geometry.
This is here a minimal configuration, but in some of these embodiments, the peripheral structure also comprises at least one small dose implantation zone of the second type of doping adjacent to the rear face, in the form of a zone adjacent to the rear junction and/or a zone adjacent to the wall.
Thus the peripheral structure advantageously comprises another implantation zone adjacent to the wall, adjacent to the rear face. The presence of this rear implantation zone is the more useful to enhance voltage handling as the rear junction and the wall are close.
This second embodiment of the peripheral structure enables easy and quick assembly, by soldering the rear field plate on a seat.
In the third embodiment mentioned above, the peripheral structure comprises:
a rear field plate covering the whole rear face,
the implantation zones adjacent to the wall, respectively adjacent to the front and rear faces,
a front field plate covering partially the front face between the connection to the cathode and the implantation zone adjacent to the wall and the front face, and
at least one first small dose implantation zone of the second type of doping adjacent to one of the junctions and to the corresponding face, whereas the peripheral structure supports at least one voltage for direct-biasing of this junction.
This structure exhibits, as in the second embodiment, substantially non-symmetrical topology. It enables nevertheless to obtain symmetrical voltage handling.
Besides both front and rear implantation zones adjacent to the wall, the peripheral structure comprises at least one small dose implantation zone, adjoining one of the front or rear junctions. In the embodiment where the substrate is of N-type, that is the rear junction for direct-bias operation and the front junction for reverse-bias operation.
Preferably, the component also comprises at least one second small dose implantation zone of the second type of doping, adjoining the other junction and the corresponding face. Thus, it enables symmetrical voltage handling.
In case when only one of the front or rear junctions is extended by one (or two) small dose implantation zone, the component is particularly suited to operation in one voltage direction. However it remains capable of operating in reverse direction as well with significantly lower maximum electrical field, whereas the insulating bow fulfils its distribution role of the equipotential lines in the substrate.
This third embodiment of the structure that enables, as the second embodiment, to solder the rear face, also allows surface reduction thanks to the presence of the front plate.
According to a preferred embodiment of the small dose implantation zones adjoining the junctions, these are of the junction termination type.
In embodiment variations, they have been selected among the guard rings, the field electrodes or field plates, the semi-resistive layers or the gradual junction terminations.
The structure is preferably of planar type.
Advantageously, the first dosing type is N and the second doping type is p.
The structure is preferably symmetrical with respect to a plane perpendicular to the front and rear faces and to the plane of the substrate.
It is advantageous that the structure should comprise field oxides covering the front and rear faces in zones excluding the junctions and including the insulating boxes. These field oxides are interposed between the front and rear faces on the one hand, and the field plates on the other hand.